(1) Field of the Invention
The present invention relates to an anti-lock braking method and apparatus for controlling a braking force imposed on wheels of an automotive vehicle. More particularly, the invention relates to an improvement of response characteristics in the braking force control to thereby obtain a stable braking performance.
(2) Related Art of the Invention
Most recent high-quality model vehicles are equipped with an anti-lock brake apparatus (hereafter referred to as "ABS") for restricting wheel slip during braking and to improve the braking thereof.
The ABS compares a wheel speed V.sub.W and a vehicle speed V.sub.B (for example, a projected vehicle speed is obtained on the basis of the wheel speed and wheel acceleration and deceleration) to obtain a wheel slip ratio S {=(V.sub.B -V.sub.W)/V.sub.B }, and the braking force exerted on the wheel is controlled so that the wheel slip ratio is maintained within a predetermined range (near 0.15-0.3) to thereby minimize a braking distance (see Japanese Patent Application No. 2-273278).
In the conventional ABS's employing the foregoing control systems, however, the braking force control is initiated after detecting a wheel slippage induced by a locked condition of the wheel and therefore, a relatively long response delay occurs from the locking of the wheel to the initiation of the brake control operation.